1. Field of Invention
The present invention relates to a liquid crystal device, a projection type display device and a method of manufacturing the liquid crystal device. Particularly, the present invention relates to a light shielding structure in a liquid crystal device comprising a thin film transistor (referred to as "TFT" hereinafter) as a pixel switching element.
2. Description of Related Art
For a conventional active matrix driving system liquid crystal device a configuration is brought into practical use in which pixel electrodes are formed in a matrix on a glass substrate and a pixel switching TFT comprising a semiconductor layer of an amorphous silicon film or a polysilicon film is formed in correspondence with each of the pixel electrodes so that a voltage is applied to each pixel electrode through the TFT to drive a liquid crystal. In a liquid crystal device comprising pixel switching polysilicon TFT, TFT'S for driving circuits comprising peripheral driving circuits such as a shift register circuit, etc. for driving and controlling a screen display portion can be formed in substantially the same process as the pixel switching TFT, and thus the liquid crystal device attracts attention because it is suitable for high integration.
In such an active matrix system liquid crystal device, in order to achieve high definition of the display, a light shielding film referred to as a black matrix (or black stripes) or the like and made of a chromium film, aluminum film, or the like is formed on an opposite substrate. The light shielding film is also formed to overlap with the pixel switching TFT so as to prevent the light incident on the opposite substrate from entering the channel region and junctions of the pixel switching TFT and prevent a leak current from flowing through the pixel switching TFT. (This light shielding film is referred to as "third shielding film hereinafter.)
However, the leak current due to light is not only due to the light incident on the opposite substrate side but also irradiation of the channel region of the pixel switching TFT with the light reflected by a polarizing plate or the like disposed on the back side of the liquid crystal device substrate.
As a method of preventing the leak current due to such reflected light (return light), Japanese Examined Patent Publication No. 3-52611 discloses an invention in which a light shielding film is also provided on the lower layer side of the channel region of the pixel switching TFT. However, in the disclosed invention, the potential of the light shielding film is not fixed, and there is thus a problem in which TFT characteristics vary or deteriorate due to the parasitic capacitance between the semiconductor layer of the TFT and the light shielding film.
On the other hand, the peripheral driving circuits are increasingly demanded to be highly integrated with an increase in the number of pixels and miniaturization of an electronic apparatus containing the liquid crystal device. Particularly, in a liquid crystal device containing the peripheral driving circuits provided on the same substrate, as a technology for achieving high integration of circuits, a multilayer wiring technology is used in which wiring is provided by forming metallic films of aluminum or the like in multiple layers with insulating films between the respective layers. However, this technology has a problem in that the number of steps and production cost are increased by forming the multilayer wiring structure.
Also, as the speed of the operation frequency of the active matrix driving system liquid crystal device increases, attempts are made to improve the quality of the semiconductor film by employing a SOI technology, a recrystallization technology using laser annealing, or the like in order to improve TFT characteristics. However, such a method of improving TFT characteristics has the problem of increasing the variations in characteristics and the problem of complicating the manufacturing process.